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Osteichthyes
| image = | image_caption = Atlantic herring | regnum = Animalia | phylum = Chordata | subphylum = Vertebrata | infraphylum = Gnathostomata | superclassis = Osteichthyes* | superclassis_authority = Huxley, 1880 | subdivision_ranks = Classes | subdivision = Actinopterygii Sarcopterygii }} Osteichthyes ( ), also called bony fish, are a taxonomic group of fish that includes the ray-finned fish (Actinopterygii) and lobe finned fish (Sarcopterygii). The split between these two classes occurred around 440 mya. In most classification systemsA Tree of Life the Osteichthyes are paraphyletic with land vertebrates. That means that the nearest common ancestor of all Osteichthyes includes tetrapods amongst its descendants. Actinopterygii (ray-finned fish) are monophyletic, but the inclusion of Sarcopterygii in Osteichthyes causes Osteichthyes to be paraphyletic. Most bony fish belong to the Actinopterygii; there are only eight living species of lobe finned fish (Sarcopterygii), including the lungfish and coelacanths. They are traditionally treated as a class of vertebrates, with subclasses Actinopterygii and Sarcopterygii, but some newer schemes divide them into several separate classes. The vast majority of fish are osteichthyes. Osteichthyes are an extremely diverse and abundant group consisting of over 29,000 species, making them the largest class of vertebrates in existence today. Characteristics Osteichthyans are characterized by a relatively stable pattern of cranial bones, rooted, medial insertion of mandibular muscle in lower jaw. The head and pectoral girdles are covered with large dermal bones. The eyeball is supported by a sclerotic ring of four small bones, but this characteristic has been lost or modified in many modern species. The labyrinth in the inner ear contains large otoliths. The braincase, or neurocranium, is frequently divided into anterior and posterior sections divided by a fissure. Bony fish typically have swim bladders, which helps the body create a neutral balance between sinking and floating. However, these are absent in many species, and have developed into primitive lungs in the lungfishes. They do not have fin spines, but instead support the fin with lepidotrichia (bone fin rays). They also have an operculum, which helps them breathe without having to swim. They also are able to see in colour, unlike most other fish. Bony fish have no placoid scales. Mucous glands coat the body. Most have scales of sort: ganoid, cycloid, or cytenoid. These scales are smooth and overlapping. Skeleton The skeleton is made of bone and cartilage, and is almost completely calcified. The vertebral column, cranium, jaw, ribs, and intramuscular bones make up the skeleton. One of the best-known innovations of the osteichthyans is endochondral bone or "replacement" bone, which is bone ossified internally, by replacement of cartilage, as well as perichondrally, as "spongy bone." In vertebrates, in general, there are various types of calcified tissue: dentine, enamel (or "enameloids") and bone, plus variants characterized by their ontogeny, chemistry, form and location. But endochondral bone is unique because it begins life as cartilage. In lower vertebrates, cartilaginous structures can become superficially calcified. However, in osteichthyans, the circulatory system invades the cartilaginous matrix. This permits the local osteoblasts (bone-forming cells) to continue bone formation within the cartilage and also recruits additional, circulating osteoblasts. Other cells gradually eat away at the surrounding cartilage. The net result is that the cartilage is replaced from within by a somewhat irregular vascularized network of bone. Structurally, the effect is to create a relatively lightweight, flexible, "spongy" bone interior, surrounded by an outline of dense, lamellar periostial bone. Since this bone now surrounds other bone, rather than cartilage, it is referred to as periostial rather than perichondral. This is the unique endochondral bone from which the osteichthians derived their name, as well as many structural advantages. However useful endochondral bone may be, it is also much heavier and less flexible than cartilage. Thus, many modern osteichthyan groups, including the extremely successful teleosts, have evolved away from extensive use of endochondral bone. Biology Most bony fish breathe through gills. Lungfish and other osteichthyan species, are capable of respiration through lungs or vascularized swim bladders. Other species can respire through their skin, intestines, and/or stomachHelfman G.S., B.B. Collette and D.E. Facey. The Diversity of Fishes. Blackwell Sciences, 1997. Osteichthyes are ectothermic (cold blooded), meaning that their body temperature is dependent on that of the water. They can be any type of heterotroph: omnivore, carnivore, herbivore, or detrivore. Some bony fish are hermaphrodites. Fertilization is usually external, but can be internal. Development is usually oviparous (egg-laying) but can be ovoviviparous, or viviparous. Although there is usually no parental care after birth, before birth parents may scatter, hide, guard or brood eggs. Examples The ocean sunfish is the most massive bony fish in the world, while the longest is oarfish. Specimens of ocean sunfish have been observed up to in length and weighing up to . Other very large bony fish include the Atlantic blue marlin, some specimens of which have been recorded as in excess of , the black marlin, some sturgeon species, the giant grouper and the goliath grouper, both which can exceed in weight. In contrast, the dwarf pygmy goby measures a minute . Arapaima gigas is the largest species of freshwater bony fish. The largest bony fish ever was Leedsichthys. See also * Ostracoderm - armoured jawless fishes. * Acanthodians - relatives of the bony fishes Category:Bony fish References ca:Osteïcti cs:Ryby cy:Pysgodyn esgyrnog da:Benfisk de:Knochenfische et:Luukalad el:Οστεϊχθύες eo:Ostaj fiŝoj es:Osteichthyes fr:Osteichthyes ko:경골어류 he:דגי גרם hr:Koštunjače it:Osteichthyes la:Osteichthyes lt:Kaulinės žuvys lv:Kaulzivis hu:Csontos halak mk:Коскени риби' nl:Osteichthyes ja:硬骨魚綱 no:Beinfisker oc:Osteichthyes pl:Ryby kostnoszkieletowe pt:Osteichthyes ru:Костные рыбы scn:Osteichthyes fi:Luukalat sk:Ryby (Osteichthyes) sv:Benfiskar tr:Kemiklibalıklar uk:Кісткові риби vi:Siêu lớp Cá xương zh:硬骨魚